1. Field of the Invention
The present invention relates to a yoke for universal joint and a universal joint.
2. Description of Related Art
In an automotive steering system, for example, an intermediate shaft for connecting a steering shaft and a steering gear such as a rack and pinion mechanism has a function to contract following the retraction of the steering gear when a vehicle collides against a front object (at primary collision). This prevents an impact of the primary collision from being transferred to a steering member such as a steering wheel.
When the intermediate shaft is contracted at the primary collision, a universal joint connecting the intermediate shaft with the steering gear and the steering shaft assumes a greater bend angle (e.g., a bend angle on the order of 60°) than a bend angle thereof while the vehicle is moving.
Since the steering member may be turned at any steering angle at the primary collision, the universal joint is required to secure the above bend angle with respect to the overall range of rotational angle of the steering member.
On the other hand, a yoke for universal joint has been proposed which is formed by punching out a sheet metal and press forming the resultant sheet metal (see, for example, Japanese Unexamined Patent Publication No. 2005-163866).
In an electronic power steering device having an electric motor for power assist disposed at a steering column, on the other hand, the intermediate shaft is designed to bear a greater load and hence, higher rigidity is required for the yoke for universal joint.
In a case where the press molded yoke is used as the yoke for universal joint, the yoke may suffer poor rigidity if the yoke is decreased in thickness in order to provide for the increase of the bend angle.
It is an object of the invention to provide a yoke for universal joint and a universal joint which feature a high rigidity and can secure a greater bend angle.